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  • 1
    Electronic Resource
    Electronic Resource
    The kinetics of NADH oxidation by complex I of isolated plant mitochondria (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 80 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The oxidation of matrix NADH in the presence and absence of rotenone was investigated in submitochondrial particles prepared from purified beetroot (Beta vulgaris L.) mitochondria. The submitochondrial particles oxidised NADH using oxygen and artificial electron acceptors such as ferricyanide (FeCN) and short-chain analogues of ubiquinone(UQ)-10, although the NADH-FeCN reductase activity was not inhibited by rotenone. NADH-oxygen reductase activity in the presence and absence of rotenone displayed different affinities for NADH (145 ± 37 and 24 ± 9 μM, respectively). However, in the presence of 0.15 mM UQ-1 where any contribution from non-specific sites of UQ-reduction was minimal, the rotenone-insensitive oxygen uptake was stimulated dramatically and the Km(NADH) decreased from 167 ± 55 μM to 11 ± 1 μM; a value close to that determined for the total oxygen uptake which itself was virtually unaffected by the addition of UO-1 [Km(NADH) of 13 ± 3 μM).The similar affinity of NADH-oxygen reductase for NADH when UQ-1 was present in both the presence and absence of rotenone, suggested that there may be only one NADH binding site involved in the two activities. A quantitative two-stage model for Complex I is postulated with one NADH binding site and two sites of UQ-reduction (one of which is insensitive to rotenone) with a common intermediate ‘P’ whose level of reduction can influence the NADH binding site. The poor affinity that rotenone-insensitive NADH-oxygen reductase activity displayed for NADH results from a limitation on the interaction of its UQ-reduction site with UQ-10 in the membrane; possibly from a low concentration of UQ-10 around this site or from steric hindrance restricting the access of UQ-10 to this reduction site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb04377.x
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  • 2
    Electronic Resource
    Electronic Resource
    Oxidation of NADH by plant mitochondria: Kinetics and effects of calcium ions (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 78 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The kinetics of NADH oxidation by the outer membrane electron transport system of intact beetroot (Beta vulgaris L.) mitochondria were investigated. Very different values for Vmax and the Km for NADH were obtained when either antimycin A-insensitive NADH-cytochrome c activity (Vmax= 31 ± 2.5 nmol cytochrome c (mg protein)−1 min−1; Km= 3.1 ± 0.8 μM) or antimycin A-insensitive NADH-ferricyanide activity (Vmax= 1.7 ± 0.7 μmol ferricyanide (mg protein)−1 min−1; Km= 83 ± 20 μM) were measured. As ferricyanide is believed to accept electrons closer to the NADH binding site than cytochrome c, it was concluded that 83 ± 20 μM NADH represented a more accurate estimate of the binding affinity of the outer membrane dehydrogenase for NADH. The low Km determined with NADH-cytochrome c activity may be due to a limitation in electron flow through the components of the outer membrane electron transport chain.The Km for NADH of the externally-facing inner membrane NADH dehydrogenase of pea leaf (Pisum sativum L. cv. Massey Gem) mitochondria was 26.7 ± 4.3 μM when oxygen was the electron acceptor. At an NADH concentration at which the inner membrane dehydrogenase should predominate, the Ca2+ chelator, ethyleneglycol-(β-aminoethylether)-N,N,-tetraacetic acid (EGTA), inhibited the oxidation of NADH through to oxygen and to the ubiquinone-10 analogues, duroquinone and ubiquinone-1, but had no effect on the antimycin A-insensitive ferricyanide reduction. It is concluded that the site of action of Ca2+ involves the interaction of the enzyme with ubiquinone and not with NADH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb02082.x
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  • 3
    Electronic Resource
    Electronic Resource
    The mitochondrial localization of hexokinase in pea leaves (1983)
    Springer
    Planta 158 (1983), S. 152-156 
    Details
    ISSN: 1432-2048
    Keywords: Hexokinase ; Mitochondrion ; Pisum (hexokinase) ; Leaf (hexokinase)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Up to 80% of total cellular hexokinase (EC 2.1.7.4) activity in pea (Pisum sativum L.) leaves was found to be associated with particulate fractions. Fractionation on sucrose density gradients showed this particulate activity to be associated exclusively with mitochondria. In the presence of glucose and ATP, the bound mitochondrial hexokinase could support rates of O2 uptake of up to 30% of normal ADP-stimulated rates. This stimulation of O2 uptake by hexokinase was completely sensitive to oligomycin, indicating that it resulted from an increase in the supply of ADP for mitochondrial oxidative phosphorylation. Spectrophotometric measurements of the mitochondrial hexokinase activity showed that ADP could support rapid rates of activity provided oxidizable substrates were also present to support the conversion of ADP to ATP in oxidative phosphorylation. Carboxyatractyloside, an inhibitor of adenine-nucleotide uptake by mitochondria, inhibited this ADP-supported activity, but had no effect on hexokinase activity in the presence of added ATP, demonstrating that the hexokinase enzyme was located external to the inner mitochondrial membrane. Oligomycin also inhibited ADP-supported activity but had no effect on ATP-supported hexokinase activity. Glucose (Km 53 μM) was the preferred substrate of pea-leaf mitochondrial hexokinase compared with fructose (Km 5.1 mM). Hexokinase was not solubilised in the presence of glucose-6-phosphate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397708
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular cloning and characterisation of grape berry polyphenol oxidase (1994)
    Springer
    Plant molecular biology 26 (1994), S. 495-502 
    Details
    ISSN: 1573-5028
    Keywords: polyphenol oxidase ; PPO ; grape ; Sultana ; biogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Polyphenol oxidase (PPO) was purified to homogeneity from Sultana grapes yielding a single protein with an apparent molecular mass of 40 kDa as determined by SDS-PAGE. A degenerate oligonucleotide primer based on the N-terminal amino acid sequence of this purified 40 kDa grape PPO protein was used to amplify a 1650 bp cDNA clone (GPO1M) by 3′ rapid amplification of cDNA ends (3′-RACE). GPO1M hybridized to a single 2.2 kb transcript from grape berry mRNA indicating the presence of further upstream sequence which was cloned using 5′-RACE PCR. The complete 1990 bp cDNA (GPO1) encodes a 67 kDa protein consisting of a 10.6 kDa chloroplast transit peptide, a 40.5 kDa catalytic unit containing two copper-binding regions and a 16.2 kDa C-terminal extension. Southern analysis suggested the presence of only one PPO gene in grapevine. High levels of gene expression were found in young developing berries, leaves and roots, but there was little expression in mature tissues. Biogenesis of PPO in grapevine tissues, appears to involve synthesis of a 67 kDa precursor protein which is imported into the chloroplast and processed to remove a 10.6 kDa chloroplast transit peptide from the N-terminus and a 16.2 kDa peptide of unknown function from the C-terminus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00039560
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  • 5
    Electronic Resource
    Electronic Resource
    Isolation of a full-length cDNA encoding polyphenol oxidase from sugarcane, a C4 grass (1996)
    Springer
    Plant molecular biology 31 (1996), S. 1233-1238 
    Details
    ISSN: 1573-5028
    Keywords: polyphenol oxidase ; PPO ; sugarcane ; browning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Polyphenol oxidase (PPO) activity in sugarcane (a C4 grass) was highest in the growing point and declined down the stalk. Sugarcane PPO with an apparent molecular mass of 45 kDa was purified to homogeneity from immature stem tissue. Western analysis of sugarcane extracts with a polyclonal antibody raised to this protein suggested it resulted from cleavage of a 60 kDa protein during purification. The antibody was used to screen a sugarcane stem cDNA library. A full-length PPO clone (sugppol) was characterised and shown to encode a 67 kDa precursor protein comprising a plastid transit sequence of 8 kDa and a mature PPO protein of 59 kDa. High levels of expression ofsugppol were detected in the growing point of the stalk and in the immature tissue immediately below it, but no message was detected in RNA from mature stem or leaf. Comparison with other PPO sequences indicated thatsugppol was significantly different to PPO genes in C3 dicotyledonous plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00040840
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